1. Field of the Invention
This application is co-pending with an application entitled "Apparatus and Method for Steering a Guideway Vehicle" filed as a provisional application on Mar. 12, 1999 simultaneously with the subject provisional application and having the same inventorship.
This invention relates to steering mechanisms for vehicles. More particularly, it relates to an apparatus for steering a vehicle to follow a track or guideway.
2. Description of the Related Art
Various types of on-track and off-track vehicles are currently used for mass transportation. Frequently, it is desirable for the same vehicle to be available for use on a track following a guideway (on-track) as well as on a roadway without the assistance of a guideway (off-track). This is especially useful for a vehicle that must be removed from a guideway and moved to another location for repair or maintenance. The term "guideway" is used herein to describe a roadway surface with a guide rail for steering a vehicle along a predetermined course.
Typically, such a vehicle follows a guide rail embedded below the roadway surface of the guideway and, as a result, certain elements of the vehicle steering mechanism, such as the guide wheels extending from the vehicle undercarriage which track the guide rail, protrude below the roadway surface of the guideway. This arrangement is not acceptable for off-track use because the roadway would interfere with the steering mechanism.
Ordinarily, a vehicle adapted for use both on-track and off-track employs a conventional design using pneumatic tires to operate on any substantially flat surface. Accordingly, when operated as an on-track vehicle, the guideway is substantially flat and a guide rail is mounted on the guideway parallel to the roadway surface for guiding the vehicle along a predetermined course.
U.S. Pat. No. 3,796,165 describes a guide following steering apparatus in which all of the components of the steering apparatus are above the roadway surface of the guideway. The apparatus uses guide followers protruding from the front and the rear of the vehicle. Each guide follower is associated with two steerable drive tires on each of two axles and the two guide followers are connected together with steering linkages. However, the vehicle is bi-directional and only the leading guide follower, whichever one it may be, controls the steering for wheels on both axles. In certain instances, such a design is undesirable because the protruding guide followers diminish the ride quality of the vehicle.
U.S. Pat. No. 3,515,405 describes an axle suspension system for transit vehicles utilizing a central guidance system comprised of four guide wheels attached to a guide frame to follow the direction of a guide rail. In the process, one axle on the transit vehicle orients to follow that guide rail. At least two axles are associated with a separate guidance apparatus and there is no interconnection between the two apparatuses. However, the arrangement disclosed in this patent illustrates a guide rail below the roadway surface of the guideway which makes off-track use of the vehicle impossible. Furthermore, this arrangement pivots the entire axle such that the wheels on both sides of the axle rotate as a unit. This requires the entire axle, axle housing and associate frame to be rotated when it is only necessary to turn the wheels of the axle.
It is an object of this invention to provide a guidance apparatus capable of following a guide rail located on a guideway at or above the roadway surface of the guideway using a central guidance platform and steerable axles to alleviate the need to turn the entire axle and axle housing when the vehicle must turn.